Shellfish remains are common in coastal and estuarine archaeological sites, but dating these samples require a correction for the “reservoir effect” a process whereby "old carbon" is recycled and incorporated into marine life especially shellfish inflating their actual age in some cases several centuries.
In recognition of this problem archaeologists have developed regional reservoir correction rates based on ocean bottom topography, water temperature, coastline shape and paired samples of terrestrial and marine objects found together in an archaeological feature such as a hearth.
The Mayan calendar used 3114 BC as their reference.
More recently is the radiocarbon date of 1950 AD or before present, BP.
Plankton absorbs, Carbon-14 from the ocean much like terrestrial plants absorb Carbon-14 from the air.
His radiocarbon dating technique is the most important development in absolute dating in archaeology and remains the main tool for dating the past 50,000 years.There are two techniques for dating in archaeological sites: relative and absolute dating.Relative dating stems from the idea that something is younger or older relative to something else.Absolute dating represents the absolute age of the sample before the present.Historical documents and calendars can be used to find such absolute dates; however, when working in a site without such documents, it is hard for absolute dates to be determined.